In direct spark ignition engines, fuel is injected directly into each combustion chamber. Accordingly, less fuel may be inducted past the intake valves than in port injected engines. Inducting fuel past the valves cleans carbon deposits which may deposit on the valves due to positive crankcase ventilation (PCV) and/or exhaust gas recirculation (EGR). Thus, reducing the amount of fuel inducted past the valves can result in increased deposits.
One approach to clean such deposits, using conventional cam timing and a throttle is described in U.S. Pat. No. 6,178,944. This approach injected fuel during a valve overlap period when the engine is throttled to draw fuel back into the intake port.
However, the inventors herein have recognized a disadvantage with such an approach. For example, this approach requires throttling which can increase pumping losses and increase fuel consumption. The additional fuel injected during vavle overlap also may increase fuel consumption since an additional injection of fuel is used. Further, in some engines, throttled conditions may be performed for an insufficient amount of the available operating range so that the opportunity to perform valve cleaning may be limited.
At least some of the above disadvantages may be overcome by a method for a vehicle traveling on the road having an engine with adjustable valve operation, the method comprising: performing a valve cleaning operation for reducing deposits on a valve of the engine; and at least during said operation, adjusting valve timing of at least a valve of the engine and a fuel injection amount to increase an amount of fuel pushed back from a cylinder past the valve with deposits and then re-inducted through the valve with deposits.
In this way, valve cleaning can be performed without requiring throttling conditions (although cleaning may be performed during throttled conditions, if desired).
An advantage of the above aspect is that fuel injected during the valve adjustments can be used to clean carbon deposits accumulated on and around an intake valve.